The present invention relates to a control device for a phase angle between two rotating members, and more particular, to a cam shaft phase adjusting apparatus for internal combustion engines, which adjusts timing, at which an intake valve or an exhaust valve driven by a crankshaft through a cam shaft is opened or closed.
Presently, the mainstream in cam shaft phase adjusting apparatuses for internal combustion engines, used in automobile engines, that is, variable valve timing controls (VTC) resides in apparatuses driven by hydraulic pressure supplied from an oil pump, which is belt-driven by an engine. Therefore, there is caused a problem that in a state, in which an engine is rotated at low speed as at the time of idling, VTC is decreased in speed of response since hydraulic pressure as supplied is low and so a sufficient driving force cannot be generated. Reduction in CO2 emission becomes important in a situation, in which regulations for exhaust gases become strict all over the world, so that it becomes necessary to improve VTC in speed of response even at the time of idling and to constantly exercise rapid control at ideal valve timing according to an operating condition.
As measures for improvement of VTC in speed of response even at low hydraulic pressure, there is proposed a cam shaft phase adjusting apparatus for internal combustion engines, described in “Variable valve timing control” of, for example, JP-A-2000-213310 and making use of fluctuating torque generated on a cam shaft over positive and negative ranges. Disclosed therein is a cam shaft phase adjusting apparatus for internal combustion engines, in which a check valve provides communication between hydraulic chambers, which vary in volume interlocking with relative rotation between a first rotating member rotationally driven by a crankshaft of an engine and a second rotating member fixed to a cam shaft, and the check valve switches over a direction, in which flow is allowed, whereby phase of the cam shaft relative to the crankshaft is changed in an optional one of both directions of retarded and advanced angles by a valve spring with fluctuating torque generated on the cam shaft as a driving force.
Also, as the related art for improvement of VTC in speed of response at low hydraulic pressure, there is proposed a cam shaft phase adjusting apparatus for internal combustion engines, described in “Valve timing control for internal combustion engines” of, for example, JP-A-2000-179315. The JP-A-2000-179315 discloses a cam shaft phase adjusting apparatus for internal combustion engines, in which an oil supply path of a hydraulic VTC to an advanced angle chamber is intermittently opened and closed in synchronous with rotation of a cam shaft to prevent fluctuating torque from generating reverse rotation in a direction of retarded angle in phase shift in a direction of advanced angle whereby speed of response is improved.
Since the check valve provided on the communication path between the hydraulic chambers permits flow of an oil in one direction but inhibits flow of an oil in the other direction in the related art disclosed in JP-A-2000-213310, however, the relative rotation between the first rotating member which interlocks with a volumetric change of the hydraulic chambers and the second rotating member which is fixed to the cam shaft is permitted in the one direction and a torque part of one of signs of that cam shaft fluctuating torque, which fluctuates over positive and negative ranges, causes relative rotation in the direction as permitted.
At this time, that mechanism, in which the check valve inhibits flow in a reverse direction, is a passive operation, in which torque of a sign in the reverse direction causes an oil to begin to counterflow to close the check valve, and certainly involves time lag. Thereby, there is caused a problem that when fluctuating torque of the cam shaft gets into high frequency at the time of high speed operation of the engine, opening and closing movements of the check valve cannot follow this and the apparatus cannot function as a phase shift apparatus. Also, there is caused a problem that a decrease in speed of response is caused corresponding to some reverse rotation generated until a reverse rotation preventing function works.
Also, the related art disclosed in JP-A-2000-179315 discloses a construction, in which intermittent oil supply achieves an improvement in speed of response mainly in the direction of advanced angle, and a construction, in which phase shift in the direction of advanced angle is switched over to a conventional, continuous oil supply by a change in hydraulic pressure. Switchover to the conventional, continuous oil supply aims at inhibiting intermittent oil supply in high speed operation, in which sufficient hydraulic pressure is obtained, from becoming conversely responsible for a disadvantage such as a decrease in speed of response, a water hammer phenomenon in hydraulic pressure paths, etc.
Since JP-A-2000-179315 does not disclose any specific construction, in which a high response at the time of phase shift in the direction of retarded angle and switchover to continuous oil supply are realized at the same time, however, there is caused a problem that the effect of high response at low speed is not ensured at the time of phase shift in both the direction of advanced angle and the direction of retarded angle and that an effect of inhibiting a disadvantage at high speed, which is obtained by switchover to continuous oil supply, cannot be ensured at the time of phase shift in both the direction of advanced angle and the direction of retarded angle.
It is an object of the invention to provide a cam shaft phase adjusting apparatus for internal combustion engines, which is excellent in practicability and high in response and which is higher in response than a conventional one at the time of low speed (low hydraulic pressure) and eliminates generation of a new disadvantage such as a water hammer phenomenon, etc. while ensuring the same, high response as that in a conventional one at the time of high speed (high hydraulic pressure) in that phase shift in both the direction of advanced angle and the direction of retarded angle, which is certainly carried out in a cam shaft phase adjusting apparatus.